1. Field of the Invention
The present invention relates to photolithography and, more particularly, to an exposure apparatus and an exposure method used to form a fine pattern in manufacturing a semiconductor device or the like, and to a semiconductor device manufacturing method.
2. Description of the Related Art
The manufacture of a semiconductor device using photolithography uses a projection exposure apparatus. The projection exposure apparatus irradiates, with illumination light, a mask pattern drawn on a photomask (reticle) and formed from a transmitting portion and light-shielding portion. The projection exposure apparatus projects light having passed through the photomask onto an object to be processed such as a silicon (Si) wafer via a projection optical system, forming a resist pattern.
The minimum transferable cycle (resolution) of the projection exposure apparatus is proportional to the wavelength of exposure light and inversely proportional to the numerical aperture (NA) of the projection optical system. At present, an argon fluoride (ArF) excimer laser beam having a wavelength of 193 nm is generally used. However, constraints on glass for use and the like make it difficult to further reduce the wavelength of exposure light. In recent years, the resolution is decreasing for a higher NA of the projection optical system, and a projection exposure apparatus whose NA exceeds 0.9 is becoming available.
A higher NA of the projection lens changes the imaging characteristic owing to a difference in light polarization state. Imaging of a fine pattern through a high-NA lens increases the incident angle of light on the surface of an object to be processed. As the incident angle becomes larger, the difference in light polarization direction more influences interference of light. There has conventionally been examined a method of polarizing light to be projected on an object to be processed by controlling the polarization state of illumination light (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 6-53120). However, it is difficult to increase the lithography margin when forming a fine pattern such as a hole pattern, failing to form a fine resist pattern into a desired shape.